The present invention relates to light strings such as are used for holiday lighting.
Strings of lights are typically wired electrically in series. Consequently, when one light burns out or is removed, all the lights in the string go out. Determining which light has burned out or finding a missing bulb takes time when the string has 50 or more lights. If the string of lights is attached to a Christmas tree, locating the “bad” bulb or missing bulb is an especially tedious task.
For a number of years, this problem has been solved, or at least avoided, by the use of shunts that allow current to pass from one of the terminals in the socket of the defective lamp to the other terminal. A shunt passes the current through the lamp and allows the remaining lamps to continue to operate. Prior art shunts are sometimes placed in the glass globe of a lamp and sometimes in its socket. The shunts inside the glass globe are typically coils of wire around the conductive elements. When the filament fails, the oxide coating on the wires that theretofore prevented direct conduction of electricity is burned off and the coil welds to the elements thereby passing current.
The shunts in the socket are also of two types, solid state and mechanical. Among the mechanical, for example, there is a set of spring contacts that are the subject of U.S. Pat. No. 6,257,740. These contacts are pushed apart when the lamp base is inserted into the socket. This type is strictly for use when the bulb (and its base) is removed. This type works well and has enjoyed commercial success.
There are a huge number of light strings manufactured and sold each year throughout the world. The number is so large that even small changes that, for example, reduce material requirements or improve safety, may make a huge difference in costs of manufacture. Accordingly, there remains a need for a better mechanical shunt for use in sockets of light strings.